Illumination systems for illuminating a display device are known per se. They are used, inter alia, in non-emissive displays, such as liquid crystal display devices, also referred to as LCD panels, which are used in, for example, television receivers, (computer) monitors, (cordless) telephones and portable digital assistants. The illumination systems can also be used in, for example, projection systems such as a digital projector, or so-called beamers, for projecting images or displaying a television program, a film, a video program or a DVD, or the like. In addition, such illumination systems are used for general lighting purposes, such as for large-area direct-view light emitting panels such as applied, for instance, in signage, contour lighting, and billboards.
Such an illumination system is, for example, disclosed in US 2005/0001537. In the illumination system disclosed in the cited US application, the illumination system comprises an array of red, green and blue light emitting diodes in a mixing chamber. In an embodiment of the illumination system, the illumination system comprises two diffusers which are separated relatively far apart so as to form two mixing chambers. The first diffuser is shown in a generally central position in the illumination system. A second diffuser, essentially forming the top of the illumination system, defines the roof of the upper mixing chamber. The lower mixing chamber provides a relatively good mixture of the light, which is then made more uniform by the first diffuser. This fairly uniform light distribution is then further mixed in the second mixing chamber. This mixed light is then diffused again by the second diffuser to create a relatively uniform light profile.
A drawback of the known illumination system is that a light-mixing chamber for mixing the light over the light exit window is relatively thick.